Open-source alternatives to Slack: 4 team chat tools compared
Running chat yourself trades Slack's per-user billing and vendor-held history for servers, databases and upgrades that belong to your team. Most readers should look at mattermost/mattermost first, since it is a single Linux binary against PostgreSQL, while element-hq/element-web only makes sense if you already run a Matrix homeserver.
What Slack does, and why people look elsewhere
Slack is hosted team messaging: channels, direct messages, threads, calls and integrations with other tools.
- message history and files are held by Slack and, on some plans, hidden after a retention window
- per-active-user pricing
- compliance and data-residency needs that require the chat server to run inside your own network
The candidates at a glance
| Project | Licence | Maintenance | Language | GitHub stars | Install |
|---|---|---|---|---|---|
| RocketChat/Rocket.Chat | Custom licenceCustom licence: read the LICENSE file | Commits in the last six monthsLast push November 7, 2026 | TypeScript | 46,374 | See analysis |
| mattermost/mattermost | Custom licenceCustom licence: read the LICENSE file | Commits in the last dayLast push November 7, 2026 | TypeScript | 39,554 | See analysis |
| zulip/zulip | Apache-2.0Permissive: commercial use allowed | Commits in the last six monthsLast push November 6, 2026 | Python | 26,187 | See analysis |
| element-hq/element-web | AGPL-3.0Network copyleft: hosting a modified version means sharing source | Commits in the last six monthsLast push November 6, 2026 | TypeScript | 13,640 | See analysis |
Each alternative in detail
RocketChat/Rocket.ChatThe Secure CommsOS™ for mission-critical operations
- Best for
- You need the chat server on hardware you control, ideally on a network with no internet access, or you need federation so conversations can cross organisational boundaries. The air-gapped deployment path and the compliance features are the reasons to pick this one.
- What you give up
- It is a monorepo with a Yarn workspace tree, so there is a build step and an upgrade path you have to rehearse before it reaches production. The repository is a monorepo with its own build and deployment tooling, and the README points at Docker, Podman, Kubernetes or Launchpad rather than a single binary, which is more than a small team wants to own. Licence terms also differ by edition, and features such as Apps-Engine and federation may sit in the community edition or in the ee/ directory, so what you can actually run depends on the release you pin.
mattermost/mattermostMattermost is an open source platform for secure collaboration across the entire software development lifecycle..
- Best for
- You need chat plus workflow automation, voice calling and screen sharing inside your own network, and you are willing to run PostgreSQL. A single Linux binary written in Go and React is the smallest server on this list to operate.
- What you give up
- It is open core, so which licence file in the repository applies decides what you actually have, and the features outside the MIT release are the ones to check against your plans. The README points at a security bulletin mailing list rather than promising automatic updates, so patching is a scheduled job your team owns. There is also a monthly release rhythm to track, which helps a team that versions its deployments and hurts one that does not.
zulip/zulipZulip server and web application. Open-source team chat that helps teams stay productive and focused.
- Best for
- Your team's conversations are mostly asynchronous and you need them to still be readable a week later. Topic threads instead of one channel stream is a deliberate design choice, and Apache-2.0 removes the licence question from the decision entirely.
- What you give up
- This is the heaviest deployment here: our analysis of Zulip names PostgreSQL, RabbitMQ, Redis and memcached, and says plainly that if nobody on the team will own that stack, this is the wrong pick. It also asks users to learn topic threads, which is a real adoption cost against a chat tool that looks familiar on day one. And a non-technical admin cannot run it unaided.
element-hq/element-webA glossy Matrix collaboration client for the web.
- Best for
- You already run a Matrix homeserver, or you want federated chat where the same conversation exists on more than one server. It is the reference web client for Matrix, and it also runs as a desktop app wrapped in Electron.
- What you give up
- It is a client, not a server, so the largest piece of work on this page is the homeserver, and it is not in this repository. The README classifies mobile web as community supported and points Android and iOS users at the native Element X apps, so a phone-first team is not served here. The repository is AGPL-3.0 and the README states the software is multi licensed under the AGPL, the GPL or a paid Element Commercial License, so how you distribute it has to be settled first.
What each project actually is: three chat servers and one protocol client
Slack is one product: hosted channels, direct messages, threads, calls and integrations with other tools. The four projects below are not four attempts at that product, and the difference matters before any feature comparison.
Three of them are chat servers you host. RocketChat/Rocket.Chat is a TypeScript platform whose README describes deployment on your own servers, in an isolated air-gapped workspace, or through federation across a federated network. mattermost/mattermost is described in its README as open core, written in Go and React, running as a single Linux binary and relying on PostgreSQL. zulip/zulip is a Python server built around topic threads rather than a single channel stream.
element-hq/element-web is different in kind. The README calls it a Matrix web and desktop client built on the Matrix JS SDK. It is a client, which means the homeserver that stores rooms and history is a separate piece of software that none of these four repositories contains. If you have never run a Matrix homeserver, choosing this is choosing a much larger project than choosing a chat server.
The other difference is conversational shape. Rocket.Chat and Mattermost are conventional channel and thread models, so people arrive already knowing how to use them. Zulip asks people to learn topics, where a conversation is split into named sub-threads inside a stream. That is a better fit for work that continues across days and a worse fit for a team that wants chat to feel like the tool it replaced.
Why Microsoft Teams and the other hosted options are not here
Microsoft Teams is the search term most readers arrive with after Slack, and it is not in the list for one reason: it is hosted. Teams, Slack and the other commercial workspace products all keep your message history and files on someone else's servers, and that is the property this page is about.
There are honest reasons to stay. If nobody on the team wants to run a database, a chat server and a patching routine, a hosted product is the correct answer and self-hosting will make things worse. Teams in particular is a sensible choice where the surrounding office suite already points at it, and nothing here is an argument against it.
Also missing is the long tail of other self-hosted chat servers that did not make this list. The selection is not a ranking, and a project absent here is not a worse project. What the four share is a public repository, a licence you can read, and a history of pushes, which is what makes an informed choice possible.
One more absence worth naming: Discord, which many teams think of as a Slack replacement, is hosted and closed, so it does not belong on a page about running the chat server yourself.
Choosing by scenario: a solo user, a small team, a regulated company, a developer embedding chat
Pick by who has to do the work, not by the feature list.
One person, or a team of two or three, should start with mattermost/mattermost. A single binary against PostgreSQL is a small number of moving parts, and the README lists install routes for Docker, Ubuntu, tar, Kubernetes and Helm, so there is a path that matches almost any environment already in use. Rocket.Chat is heavier for a small team: the repository is a monorepo with its own build and deployment tooling, and the command shown on this page, yarn dev, is a development command rather than a deployment, which is itself a signal about what running it involves.
A company with compliance requirements is the clearest case for RocketChat/Rocket.Chat. The README describes an air-gapped workspace for running without internet access, a compliance center, end-to-end encryption, and role and attribute-based access control. Message residency inside your own network is the whole point, and this is the project that treats it as a first class requirement.
A team whose conversations are mostly written rather than spoken should look at zulip/zulip. The design is built for reading later, with topic threads that let a stream carry many separate conversations. The cost is real administration: our analysis of Zulip names PostgreSQL, RabbitMQ, Redis and memcached, and says plainly that if nobody on the team will own that deployment, this is the wrong choice.
A developer embedding chat into a product, or a group that wants conversations to cross organisational boundaries, is the case for element-hq/element-web. Federation is the reason it exists in this form, and if you need it, nothing else on the list does it.
What each server costs to operate month after month
The install commands and repository shapes tell you most of what follows.
mattermost/mattermost has no single install command in our analysis, which means the deployment choice is the work: Docker, Omnibus, a tar install, an Ubuntu package, Kubernetes or Helm. Underneath is one Linux binary and one PostgreSQL database, and that is the honest floor. The README states a new compiled version is released under an MIT license every month on the 16th, and it also points at a security bulletin mailing list rather than promising automatic updates. Patching is a recurring job your team schedules, and the monthly cadence makes it a regular one.
RocketChat/Rocket.Chat is a monorepo with a Yarn workspace tree, and the README sends you to Docker, Podman, Kubernetes or Launchpad, where Launchpad is described as a way to set up Kubernetes without managing each dependency. A monorepo means a build step, which means the upgrade path is yours to rehearse before it touches production.
zulip/zulip has no single install command in our analysis either. The documented routes are Ubuntu or Debian Linux directly, in Docker, or prebuilt images for Digital Ocean and Render. Behind that sit four services to keep healthy, which is the highest operational load of the three servers on this page.
element-hq/element-web is a static client, so hosting it is cheap, but you still have to run and patch a homeserver, and that homeserver is the expensive part. Read docs/config.md for the settings your deployment needs, and remember the repository is a pnpm monorepo.
Licences, from Apache-2.0 to Element's multi-licence arrangement
Three of these four are straightforward for a company. One is not.
zulip/zulip is Apache-2.0, and the README states that plainly. You can run it, modify it, and offer the modified version as a service, with the usual obligation to carry the licence text forward.
mattermost/mattermost is open core. The README states that a new compiled version is released under an MIT license each month, and the repository carries more than one licence file, so the practical question is which features your deployment plans to enable and which of them fall under commercial terms. Answer that before you commit, not after a feature request is denied.
RocketChat/Rocket.Chat uses a licence GitHub cannot classify from the repository metadata alone, and the features you want may sit in the community edition or in the ee/ directory depending on the release. The practical step is to read the licence terms for the edition you intend to run, and to check where Apps-Engine and federation land in the version you pin.
element-hq/element-web is the one to slow down on. The repository is AGPL-3.0, and the README states that the software is multi licensed: the GNU Affero General Public License, the GNU General Public License, or a paid Element Commercial License agreement whose terms vary by arrangement. AGPL-3.0 is the part that matters for a company. If you host a modified version of the client on a network, the copyleft obligation reaches users of that instance. That is manageable for internal deployment and a different conversation entirely for a product you ship. The README also points licensing questions to a contact address, and that is the right place to get an answer before you build on it.
Bottom line
For most teams the order is mattermost/mattermost first, RocketChat/Rocket.Chat when the network is isolated or the regulator is involved, zulip/zulip when conversations are written and somebody will own four services, and element-hq/element-web only with a homeserver already in place. Before committing, confirm which licence file covers the features you intend to enable, read the deployment guide that matches your environment, and name the person who patches the server and reads the security bulletins.
Sources
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